Wireless communication is an increasingly popular means of personal communication in the modern world. People are using wireless networks for the exchange of voice and data as an alternative to using a wire infrastructure. In principle, a user can seek information over the Internet or call anyone over a public switched telephone network (PSTN) from any place inside the coverage area of the wireless network.
In a typical wireless network, an area is divided geographically into a number of cell sites, each defined by one or more radiation patterns created by an emission of radio frequency (RF) electromagnetic waves from a respective base transceiver station (BTS) antenna. For wireless communications, RF signals are not sent through a transmission line and, therefore, antennas are required for the transmission and reception of the signals.
Cellular networks provide a communications path between each subscriber's mobile phone and a mobile switching center (MSC). The MSC manages communications to and from mobile phones in a variety of locations. Typically, several base stations are affiliated with each MSC, and each mobile phone communicates through a BTS that is nearby relative to other base stations. As the mobile phone changes location (when, for example, its user is driving in a car), it may also change the BTS through which it communicates.
Each BTS has a backhaul facility, through which it communicates with the MSC to carry mobile telephone conversations within the cell. The backhaul facility typically communicates with the MSC through either a microwave link or a terrestrial wire, such as a T-1 line.
To provide a high quality of mobile phone service, it is desirable for cells to be adjacent to one another, leaving no intermediate gaps in which cellular phone service is unavailable. Likewise, each cell could be arranged such that its corresponding BTS has the capacity to handle all the telephone conversations carried out by users at peak times within the cell. Thus, a central business district in which many mobile telephones are used during the business day is typically provided with a higher density of base stations, each with a smaller cell, than in outlying areas.
Designing a cellular network for a high quality of service involves a number of issues. For example, to avoid gaps in service areas, so-called “coverage holes,” it may appear desirable to design larger cells that are served by base stations with high-power antennas. However, the larger cell would encompass more subscribers and may cause calls to be dropped if the capacity of the BTS is exceeded. Another solution—increasing the number (and, accordingly, the density) of base stations—entails a financial expense, the regulatory and architectural challenge of finding (and leasing) a desirable location for each BTS, and the task of arranging for backhaul communications from each new BTS to the MSC.
To provide flexibility in the design of mobile telephone networks, remote antenna systems or distributed antenna systems (DAS) have been utilized. One example remote antenna system is the digivance long-range coverage solution (LRCS), from ADC Telecommunications, Inc., of Minneapolis, Minn.
A remote antenna system may correspond to a particular BTS, but it can be positioned remotely from its corresponding BTS. Several remote antennas can be associated with each BTS, allowing the cell associated with the BTS to extend into controlled areas. For example, if the mobile telephone service provider determines that there is a coverage hole between two existing cells, it can position a remote antenna within that hole and associate that remote antenna with an existing BTS.
Remote antenna systems may also be used to bring RF coverage inside and throughout a facility, underground (for example, within tunnels), or anywhere that outdoor RF signals do not reach. Prior to the development of an in-building wireless (IBW) network or a DAS, in order to access the cellular network from inside a building one had to hope that a local cellular carrier's network could penetrate exterior and interior walls of the building from the outside. More often than not, one would need to go outside to make or receive a call.
A remote antenna system or DAS varies from a small repeater or enhancer system providing service for individual subscribers or covering two or three floors of a small office block to large scale systems using a BTS to cover indoor and outdoor coverage areas. A DAS uses fiber cable within buildings to actively distribute signals to a network of small powered antennas. The system still requires a BTS in the building or nearby, but allows for signals to be sent throughout the building more efficiently and more reliably by transmitting the signals from multiple locations within the building. As such, a DAS may comprise, for example, any network of components that receives an input RF signal from a BTS, converts it to wired (e.g., copper wire, optical, coax, etc.) or possibly wireless media, transports it throughout a facility, and then re-converts it back to an RF signal for transmission inside the facility.
Although remote antenna systems provide additional flexibility to mobile telephone service providers, the service provider operating in the cellular network must still arrange for communications between the BTS and the remote antenna system. These communications typically take place over a fiber optic line. As a result, the service provider typically must arrange for a terrestrial path between the remote antenna system and the BTS.